High-dielectric constant (high-k) thin films such as SrTiO3 (STO) and Ba(Sr)TiO3 (BST) have been widely investigated as one of the promising capacitor materials of the next generation dynamic random access memory (DRAM) devices. For this application, very conformal deposition with respect to the film thickness and composition is required over a 3-dimensional (3-D) capacitor structure.
Recently, atomic layer deposition (ALD) processes have been developed to meet these requirements using various source materials. ALD is one of the most promising techniques based upon its unique self-limiting deposition mechanism. In general, ALD can show low deposition temperature, excellent step coverage over high aspect ratio features, good thickness uniformity and accurate thickness control by means of layer-by-layer film deposition.
Plasma enhanced ALD (PEALD) has also been developed due to its advantages, such as higher deposition rate and lower deposition temperature, while keeping advantages of ALD.
Regarding precursor materials, for example, STO thin film can be deposited with Sr bis(2,2,6,6-tetramethyl-3,5-heptanedionato), i.e., (Sr(thd)2) as a Sr precursor, TTIP(Ti-tetraisopropoxide) as a Ti precursor and O3, O2 plasma or H2O vapor as an oxidant. Especially regarding Sr precursor, although Sr(thd)2 and some other Sr precursors have been widely studied, those precursors still have limitations, such as too low vapor pressure, thermal decomposition at low temperature, etc.
Therefore, a demand still remains for developing an appropriate Group 2 or Group 4 precursor and corresponding deposition process, most importantly finding Group 2 and 4 complexes that have similar ligands, which make them compatible in terms of physical and chemical properties, such as melting point, solubility, vaporization behavior and reactivity towards a semi-fabricated semiconductor surface. Consequently, the Group 2 and 4 complexes can be dissolved in a solvent and delivered into a reaction chamber to deposit a multi-component metal oxide film for DRAM applications.